A carefully modulated energy supply is of central importance to human health. Under condition of stress, defects in the regulation of energy output can lead to serious impairment of numerous vital processes or even to death. Yet, the pathways by which mitochondria adjust the rates of oxygen consumption and ATP production in response to extrinsic signals are not well understood. The long term objective of the proposed research is the elucidation of these signal pathways. Studies in this laboratory have led to working model of a bicyclic cascade system that can explain at the molecular level how mitochondria recognize and meet changing energy demands. The essence of the model is a transduction and amplification of cellular signals into the altered covalent phosphorylation of the mitochondrial sulfurtransferase, rhodanese; the rhodanese forms, in turn, serve as converter enzymes which directly alter the rate of the respiratory chain and, thus, ATP production by the reversible sulfuration of iron-sulfur centers. It is planned to test basic features of the model in bovine and rat liver. Towards this goal, the effects of dephospho- and phosphorhodanese substrates; phosphorhodanese, the rhodanese kinase, the rhodanese phosphatase and a rhodanese- multiproteins complex that forms iron-sulfur centers will be isolated and characterized by standard techniques of protein chemistry; effectors for the enzymes will be identified in kinetic studies; hormonal effects on the enzyme activities will be examined in perfused liver or isolated mitochondria and where applicable, second messengers will be identified. In addition, an E. coli rhodanese which is half the size of the mitochondrial enzyme will be characterized and its relationship to the bacterial respiratory chain will be examined in physiologic and genetic studies. The proposed studies have good potential to be of far-reaching importance for the understanding of energy metabolism. They should establish the pivotal role of sulfuration/desulfuration by the rhodaneses in the regulation of oxidative metabolism.